On Tuesday, February 23, 2021 at 9:47:53 PM UTC-8, wrote:
At the Cowley wave camps, there's the odd day when record attempts are made to 30,000+ It gets really cold up there as in -30C - actually surface temperature at night a week or so ago.

My welding supplier advises ABO for that kind of height and temperature, and I'm inclined to believe him. But the turnaround time for ABO cylinders is really slow here.

Your welding supplier is confused. **there is no difference** This is the perennial noise that comes up on r.a.s every few years. All the O2 in these uses comes from cryogenic fractional distillation. The cyrogenic process freezes out all moisture. All those cylinders are filled from the same liquid oxygen source. Oxygen distribution systems are inherently dry. If they had moisture in them we'd have a boat load of safety issues in handling and distribution.